Finger identification method and apparatus

ABSTRACT

An image pickup scheme capable of always providing an optimum quality of a blood vessel pattern, in image pickup of a blood vessel pattern of a finger using transmitted light, without being affected by a difference, if any, in an external environment. A personal identification apparatus includes light sources for irradiating light to be transmitted by a finger, an image pickup unit for picking up an image using light transmitted by the finger, finger detection unit for detecting that the finger exists in a predetermined position, finger region extraction unit for extracting a region occupied by the finger from an image picked up by the image pickup unit, and gain changing unit for changing an amplification factor of image pickup elements in the image pickup unit on the basis of a picture quality of a specific region within the extracted region.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention is related to U.S. application Ser. No. 10/617,828filed Jul. 14, 2003, the entire content of which is incorporated hereinby reference.

INCORPORATION BY REFERENCE

The present application claims priorities from Japanese applications JP2005-245241 filed on Aug. 26, 2005, JP 2004-321454 filed on Nov. 5,2004, the contents of which are hereby incorporated by reference intothis application.

BACKGROUND OF THE INVENTION

The present invention relates to a personal identification apparatususing a living body. In particular, the present invention relates to abiometric personal identification apparatus based on a blood vessel(vein) pattern of a finger.

As a security scheme that does not need carrying a key or the like, thatis high in convenience, and that is little fear of illegal use such asloss and theft, attention is paid to biometrics using a part of anindividual's body, such as a finger print, iris, a blood vessel (vein)pattern. Among them, the identification method using a blood vesselpattern does not remind of criminal investigation unlike theidentification method using a fingerprint. The identification methodusing a blood vessel pattern does not irradiate light directly to aneyeball unlike the identification method using iris. Therefore, theidentification method using a blood vessel pattern causes littlepsychological resistance feeling. Furthermore, since the blood vesselpattern is not a feature of a living body surface which can be observedeasily, but it is an inside feature, the identification method using ablood vessel pattern has an advantage that the residual property is notpresent and forgery is difficult.

Such a blood vessel pattern within a living body is obtained byilluminating a target region with near-infrared light sources andpicking up an image of the target region with an image pickup system,such as a camera or an image sensor, having a sensitivity fornear-infrared light (see, for example, US2004/0184641). Since hemoglobinin blood absorbs near-infrared light well, light is absorbed by a bloodvessel and the blood vessel is taken dark as compared with a peripheraltissue. A pattern generated by the difference between brightness anddarkness becomes the blood vessel pattern.

In such a scheme for picking up an image of a blood vessel pattern usinglight, existence of light other than light from the infra-red lightsources for image pickup, i.e., external light remarkably affects thequality of the blood vessel pattern image picked up. In most biometricschemes using light used heretofore, therefore, restrictions have beenimposed on the use condition under the external light. For example, whenthe biometric scheme is used outdoors in clear weather, light havingnear-infrared wavelengths is also included in naturally existingsunlight and its intensity is far higher than that of the output of thelight sources for blood vessel pattern image pickup. If sunlight streamsinto an identification apparatus including a camera adjusted so as to beable to optimally pick up an image of a slight difference between brightlight and dark light as a pattern, luminance of many pixels is saturatedat its maximum value because of intense light, and an image including asaturated highlight region is obtained. In such a saturated highlightregion, the luminance is uniquely at the maximum value. Therefore, thedifference between brightness and darkness in the blood vessel portiondoes not appear, and a correct blood vessel pattern cannot be obtained.

In the invention described in US2004/0184641, a method of adjusting thebrightness of the light sources for image pickup according to variousfinger states has been disclosed as the method for picking up an imageof a blood vessel pattern clearly. However, the method is premised onthe indoor use, and the supposed range of the external light variationis also limited. Under the intense external light as described above,the saturated highlight region cannot be eliminated in many cases evenif the intensity of the light sources is minimized. Furthermore, in thecase described above, light irradiated to the finger cannot be utilizedsuitably although it has a quantity enough to pick up an image of theblood vessel pattern. As a result, energy is supplied to the lightsources dedicated to image pickup unnecessarily.

A conceivable solution to the problem is to eliminate the saturatedhighlight region by using sensitivity adjustment, such as the exposureor iris of the image pickup camera, together. In ordinary photographingas well, the sensitivity, such as the exposure or iris, of the camera isadjusted and the brightness of illumination such as the light issuitably changed. Basically, this should be conducted automatically. Nota few cameras have a mechanism called AGC (auto gain control) as astandard component. The AGC is a function of amplifying an output ofimage pickup elements, such as CCDs (Charge-Coupled Devices), in acamera to bring the output into a predetermined voltage range.Specifically, the amplification factor of the amplifier is automaticallyadjusted. The amplification factor is increased when the output of theimage pickup elements as a whole is low. Conversely, the amplificationfactor is decreased when the output is high. As a result, it becomespossible to automatically obtain an optimum picture quality according tothe brightness of the image pickup target.

However, the mere application of the AGC to the camera for picking up animage of a blood vessel does not make it possible to obtain a clearblood vessel pattern. The blood vessel pattern cannot be obtained untillight of a suitable quantity is transmitted. Therefore, suitable imagepickup is impossible unless the sensitivity is controlled after it isascertained well that light for picking up an image of the blood vesselpattern is sufficiently supplied. Conversely, if the light source poweris fixed without conducting light source power control at all, lightcontinues to be added from the light sources even if intense externallight is present. As a result, the saturated highlight region in theimage pickup region is further aggravated, and departure from a range inwhich the saturated highlight region can be eliminated by thesensitivity control is also caused. It is necessary to suitably controlthe power of the light sources dedicated to irradiation for image pickupand the sensitivity of the camera according to the situation so as tocause a living body region to be picked up as an image to always producea constant picture quality. Unless there is such cooperation, the powerof the light sources and the sensitivity of the camera might interferewith each other in attempting a suitable picture quality and eventuallyconvergence to a suitable picture quality might be not attained.Furthermore, in the ordinary AGC, picture quality control is exercisedto optimize the picked up image as a whole. Therefore, the fingerportion in the picked up image does not necessarily become optimum inpicture quality. For example, when a great difference is caused inbrightness between the inside of the finger and the background byexternal light, or when only a portion of the finger directly exposed tolight from the light sources for image pickup is locally bright, thegain is set to an excessively low value by strong influence of thebrightness and consequently the finger portion for which an optimumpicture quality should be originally obtained becomes too dark in itsimage. It is also conceivable to restrict an image range in which it isdetermined whether the picture quality is optimum. At the time ofidentification, however, the finger is placed or detached. Even if thefinger is placed stationarily, the finger is not always placed in thesame specific position. Therefore, the brightness of the picked up imagehas an infinite variety according to states of the finger.

Even if external light having intensity enough to obtain the bloodvessel pattern is applied to the finger, it cannot be utilizedsufficiently in situations where the light source power control and thesensitivity control in the AGC or the like operate asynchronously. Forexample, if the AGC operates when the power of the light sources forimage pickup is high and an optimum picture quality is attained, therewas a possibility that the light source power could be lowered if thegain was raised. This is wasteful energy consumption. Especially in thecase of energy supply using a battery or the like, the sustaining timeof the battery is shortened and there is a problem from the viewpoint ofpreservation of the global environment as well.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an image pickup schemecapable of always providing an optimum quality of a blood vessel patternwithout being affected by a difference, if any, in an externalenvironment ranging from an ordinary indoor environment to an outdoorenvironment in which remarkably intense external light is present.

Another object of the present invention is to actively utilize externallight as one of the light sources for picking up an image of a bloodvessel pattern and thereby enhance the energy saving performance.

A representative example of the present invention disclosed to achievethe objects is a personal identification apparatus including lightsources for irradiating light to be transmitted by a finger, an imagepickup unit for picking up an image using light transmitted by thefinger, finger detection means for detecting that the finger exists in apredetermined position, finger region extraction means for extracting aregion occupied by the finger from an image picked up by the imagepickup unit, and gain changing means for changing an amplificationfactor of image pickup elements in the image pickup unit on the basis ofa picture quality of a specific region within the extracted region.

To be more precise, there is disclosed a configuration including meansfor selecting a specific region in the gain changing means according toan output state of the light sources, and means for causing a change ofan amplification factor in the gain changing means in combination with apower change of the light sources.

According to the present invention, the power control in the lightsources for image pickup and the sensitivity control in the image pickupunit are adaptively combined according to the situation regardless ofthe external light around the identification apparatus. As a result, thefinger portion in the picked up image is controlled to have an optimumpicture quality. Therefore, the blood vessel pattern in the imagebecomes clear, and the identification precision can be improved.Furthermore, since external light is utilized as one of the lightsources for image pickup, the energy consumption quantity required forthe identification can be reduced.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of an apparatus form for implementing thepresent invention;

FIG. 2 shows an example of an apparatus system configuration forimplementing the present invention;

FIG. 3 shows an example of a software flow for implementing the presentinvention;

FIG. 4 shows an example of an optimum region for making a picturequality decision of a finger;

FIG. 5 shows an example of a structure for preventing reflection withinthe apparatus;

FIG. 6 shows an example of a flowchart showing a part of the flow shownin FIG. 3, in more detail;

FIG. 7 is a graph showing relative energy power of sunlight as afunction of its wavelength;

FIG. 8 shows an example of a filter for preventing entry of externallight from an oblique direction;

FIG. 9 shows an example of an identification apparatus according to thepresent invention attached to an instrument panel of an automobile; and

FIG. 10 shows an example of an identification apparatus according to thepresent invention attached to a door handle of an automobile.

DESCRIPTION OF THE EMBODIMENTS

Hereafter, an embodiment of the present invention will be described indetail.

FIG. 1 is a schematic diagram of an identification apparatus 100, whichimplements the present invention. On a top surface of a main body, thereis a guide groove 108, which exhibits a place to place a finger 102therein in an intuitively understandable form. Light source units 104are disposed on the left and right sides of the guide groove 108. Thisguide groove has a function of serving as a low light shielding wallthat hides the lower half side of the finger. It is possible tophysically shield external light that streams from a low position intothe finger. A blood vessel pattern to be picked up as an image ispresent on the lower half side of the finger. When light irradiated fromthe left and right light sources is scattered in the finger and outputfrom the lower side of the finger, a pattern based on the contrastbetween brightness and darkness is formed by a difference in lightabsorption quantity caused by presence/absence of a blood vessel. If atthis time intense external light directly enters toward the lower halfside of the finger, light emitted from the light sources and transmittedthrough the finger is canceled by the external light and consequentlythe blood vessel pattern becomes unclear. The light shielding wallprevents inflow of unnecessary external light. Since at the same timethe upper part is completely opened, it is easy to place the finger in apredetermined position and it is possible to actively lead the externallight to the upper half side of the finger. Because all light incidenton the upper half side of the finger can be utilized as a light sourcefor picking up an image of the blood vessel pattern on the lower halfside of the finger. In this way, the apparatus has a structure that doesnot expose the identification apparatus as it is to the external light,but leads effective light in an easily usable form, and that can shieldunnecessary light. Thus, the apparatus has a feature that the energysaving performance is enhanced by actively utilizing the external light.

Light sources 114 are disposed within the apparatus. Upper surfaces ofthe light sources 114 are covered. Light from each of the light sources114 is irradiated toward the finger placed on the guide groove 108through a light source opening unit 106. The covers disposed over thelight source units also play a role of preventing light spread outsidethe desired irradiation direction from being reflected by a finger otherthan the finger to be identified or the palm and affecting the imagepickup as disturbance light. When the finger is placed according to theguide groove 108, there is a button switch 118 in a position that comesin contact with the fingertip. The user can use the button switch 118 tosubjectively indicate timing for conducting identification itself orexercising some control together with the identification. This switchmay be a touch sensor or the like, which detects that the finger hasbeen placed on the guide unit and controls to start predeterminedprocessing in the identification. Conversely, if a scheme forsuppressing the rejection of the person himself or herself by conductingthe identification processing on a finger detected once many times in apredetermined time is adopted, the switch may not be provided. An imagepickup opening unit 110 is disposed so as to correspond to a portion ofthe finger including the first and second joints, and the image of thefinger can be picked up from a camera (image pickup unit). In general,in the blood vessel pattern of the bulb of the finger, the fingertipside is thin and unclear in many cases. Therefore, it is easier toobtain a stable identification result by conducting the identificationusing the above-described region. A band-pass filter for passing throughonly wavelengths in the near-infrared region is attached to a camera(image pickup unit) 112 to prevent light in a visible light region fromaffecting the picked up image and pick up an image of a blood vesselpattern clearly. The wavelength of the light sources 114 can be selectedso as to contain only a component required to pick up the image of theblood vessel because they are produced artificially. On the other hand,when conducting identification using external light as a light source,it is also possible to selectively lead only light in a wavelengthregion effective to picking up an image of the blood vessel fromexternal light having a wide wavelength region by using the band-passfilter and obtain wavelength characteristics similar to those of thelight sources 114. As a result, it is possible to reduce the differencebetween the illumination condition obtained when external light is usedand that obtained when the light sources 114 are used, and it becomeseasier to always sustain the stable picture quality in a predeterminedvariation range. Light shielding partitions 116 are provided to preventlight from the light sources 114 from leaking out to the camera 112. Theimage pickup opening unit 110 is covered by transparent glass or acrylicboard together with the light source opening units 106 to prevent aforeign substance from getting in the identification apparatus whilepassing through light emitted from the light sources and transmittedthrough the finger. It is also possible to put two functions, i.e.,apparatus protection and visible light removal into one board, by usinga board of an optical filter for passing through light in the infra-redregion, instead of the glass or acrylic board. In addition, the cabinetinclusive of the light source opening units and the image pickup openingunit may be formed integrally using an optical filter material. Anoptical sensor 120, such as a photodiode or a phototransistor, having ahigh sensitivity in the near-infrared is disposed near the camera 112 tomeasure the physical intensity of light streaming into the camera. Asdescribed later, the sensitivity is controlled on the basis of a resultof the measurement conducted in the optical sensor so as to make itpossible for the camera to always sustain the picture quality in apredetermined range even if the intensity of the external light changes.An auxiliary light source 122 is used to detect approach of the fingerwithout contact. The auxiliary light source 122 is disposed so as toirradiate light toward the opening unit 110.

FIG. 2 shows an example of a schematic block diagram of a systemconfiguration that implements the present invention. A finger 102 isinserted in a position to which light is irradiated from the lightsources 114. An image signal of a blood vessel pattern is acquired by acamera 112. The image signal from the camera 112 is converted to digitaldata by an image input device 200. The digital data is stored in amemory 208 via an input-output interface 204 in a computer 202. A switch118 is also connected via an input-output interface in the same way tonotify a CPU 206 of its on/off state. The CPU 206 periodically conductsprocessing on the image supplied from the camera to detect the fingerwhile controlling an optical sensor 120 and an auxiliary light source122. After the detection, the CPU 206 determines the sensitivity of thecamera 112 and the optimum power of the light sources 114 so as tooptimize the picture quality of the finger portion, and controls abrightness controller 216 and a sensitivity controller 218. When theoptimum picture quality has been obtained, the CPU 206 extracts a bloodvessel pattern and executes identification processing. And on the basisof a result of program processing, the CPU 206 exercises various kindsof control to display the result on a display device 210, send asuitable signal to a control target 214 to open/close a door, andrelease an immobilizer to start an engine. It is also possible to makeineffective the function of a credit card mounted on an automobile forthe purpose of the ETC (Electronic Toll Collection System) for tollroads until the person himself or herself is identified. Even if anautomobile is stolen, therefore, secondary damage caused by illegalpurchase can be prevented. Besides them, it is also possible to causethe CPU 206 to conduct various kinds of processing according to a resultof collation between an image pattern of the blood vessel picked up bythe image pickup unit and registered patterns. A keyboard 212 can beused to input auxiliary information concerning the identification, suchas a secret identification number. The security level can be furtherraised by requesting input of the secret identification number or thelike. If registered images used for the identification are associatedwith the secret identification number, the number of the registeredimages used for the identification can be reduced and consequently theprocessing speed can be improved. As a matter of course, it is alsopossible to connect an external information device such as an IC card222 via a card reader-writer 220 as occasion demands, store a registeredpattern in a card that is excellent in security such as tamperingresistance, and use the registered pattern. Especially in the case of anIC card, it is also possible to conduct a part or the whole of theabove-described identification processing in the card. As a result, itbecomes unnecessary to put out the registered patterns to the outside ofthe card, and consequently the security can be further enhanced from theviewpoint of personal information protection.

FIG. 3 shows an example of a software flow executed by the hardware,particularly the CPU 206. In a process 300, an initial value issubstituted into a temporary variable required for initialization of thewhole program and program execution. If a shift to the initial state iscompleted, it is detected on the basis of an image input from the camera112 whether a finger has been inserted (302). Here, detection isconducted on the basis of the image without using a touch sensor such asa button switch. At a stage in which the finger does not arrive at apredetermined position in the apparatus, therefore, the finger can bedetected earlier. As a result, the start time of the sensitivity andlight source power control can be made earlier. When the finger hasarrived at a predetermined position, a smooth shift to featureextraction processing can be conducted in the state where optimumparameters have been set. Thus the identification response time felt bythe user can be shortened. As a matter of course, a configuration inwhich the identification is started by touching the button switch 118may also be used.

For detecting the finger by conducting image processing on the basis ofthe camera image, basically it is necessary only to detect a temporalimage change between the case where the finger is present and the casewhere the finger is not present. Therefore, the auxiliary light source122 serving as a light source for finger detection is provided, and thefinger is detected by a change in an image picked up by using light fromthe auxiliary light source 122.

In particular, if the auxiliary light source 122 is set to irradiatelight from the predetermined position in which the finger should beplaced, to a space over the position, an image change can be made moreconspicuous. If the finger approaches the predetermined position, thefinger is illuminated bright by the irradiated light. If the finger isnot present or the finger is distant, the light does not arrive at thecamera and consequently a dark image is picked up. That is the reasonwhy the image change can be made more conspicuous. In addition, if theauxiliary light source 122 is turned on and off, presence of the fingercauses the following change to appear clearly. In other words, when theauxiliary light source 122 is on, a region illuminated brightly is foundin a picked up image. On the other hand, when the auxiliary light source122 is off, the region becomes dark. If the finger is not present or thefinger is distant, the image remains dark and there is little change,regardless of whether the auxiliary light source 122 is on or off. Byutilizing this, the finger can be detected with relatively highprecision. By the way, the light sources 114 for picking up an image ofthe blood vessel pattern can be used for finger detection as well,resulting in a reduced component cost. On the other hand, the lightdirection of the light sources 114 must be set so as to illuminate thefinger optimally when the finger is placed in the predeterminedposition. Therefore, a change in the image caused by emission of lightis hard to occur until the finger arrives at the predetermined position.On the way of the finger approaching the predetermined position,reaction is not caused. Therefore, detection of the finger is delayed,and the processing time felt by the user becomes long. By separatelyproviding the auxiliary light source and irradiating light toward aplace where the finger passes through before it arrives at thepredetermined position, it becomes possible to detect the finger at anearlier point in time. If the image pickup range of the camera isexposed to intense external light in the situation where the lightsource for finger detection is set and the camera has been controlled tohave a sensitivity capable of detecting a minute difference betweenbrightness and darkness, there is a fear of producing an image includinga saturated highlight region in which the luminance is always saturatedat a maximum value regardless of whether the finger is present andwhether the auxiliary light source is on. In this state, an image changeaccording to the presence/absence of the finger is not generated. On theother hand, if the gain is lowered excessively, a saturated shadow imagein which the luminance becomes always the minimum value is obtainedregardless of whether the finger is present and whether the auxiliarylight source is on. Eventually, an image change according to thepresence/absence of the finger is not obtained. In the presentembodiment, therefore, a configuration for finding a gain value suitablefor the environment, such as irradiation of external light, in which theapparatus is placed is also provided and the gain control of the camerais conducted (306).

For obtaining the gain value, the optical sensor 120 disposed in closevicinity to the camera is used in the present invention. A physicalabsolute quantity of light that streams into the camera via the opticalsensor is found, and a gain value optimum for the finger detection iscalculated on the basis of the absolute quantity. Specifically, acircuit is formed using elements, such as photodiodes orphototransistors, having electrical characteristics that changeaccording to the light intensity. And a change of an output voltage ofthe circuit is converted to a digital value by an A-D converter, and thedigital value is taken into the CPU as data. The CPU finds a gain valueto be set, using a look-up table or a predetermined function expression,on the basis of the data, and conducts setting for the camera. As aresult, the optimum gain value can be found instantaneously. At thistime, the CPU controls timing so as to conduct gain setting only whenthe auxiliary light source is off. Because light from the auxiliarylight source 122 affects the optical sensor 120 and a correct externallight state cannot be acquired when the auxiliary light is on. Unlikethe ordinary AGC function, a relation expression between the output dataof the optical sensor and the gain setting value is found on the basisof whether the image change caused by the presence/absence of the fingerbecomes the maximum, instead of the superiority or inferiority inpicture quality. This aims at facilitating the image acquisition of thefinger.

For searching for a suitable gain value while judging the image, itbecomes necessary to verify several images to attain convergence to anoptimum value. If a change such as going in and out of the finger occursduring that time, there is a possibility that it will not be able tofind a suitable gain value. According to the above-describedconfiguration of the present invention, however, the setting time isshort and there isn't such a fear.

As another embodiment for detecting the finger, the output value of theoptical sensor can be used as it is. If external light streaming intothe camera is intense, the output value of the optical sensor remarkablychanges according to whether the finger is not present and light comesin directly, or the finger is held up and the finger shields directirradiation like an umbrella. This change is utilized for fingerdetection. As a matter of course, it is desirable to use the change ofthe output value obtained only when the auxiliary light source is off,at this time as well. When the external light is weak, however, thefinger detection using the image is more suitable, because a change inquantity of light incident on the optical sensor caused by thepresence/absence of the finger is small and consequently it is difficultto discriminate a change in the output value of the sensor from anillumination change in the surroundings.

It is also possible to use the finger detection method utilizing thesensor and the finger detection method utilizing the camera image bycombining them with each other. For example, if the sensitivity of thecamera cannot be completely controlled to become sufficiently low underintense external light, approach of the finger cannot be detected usingthe image. However, the approach of the finger can be detected bydetecting a change with the sensor. By exercising control again to lowerthe sensitivity on the basis of the detection, modification can also beconducted so as to make it possible to pick up an image of the fingerprecisely.

In the above described example, the optical sensor is disposedseparately from the image pickup elements. Alternatively, it is alsopossible to use the output itself of the image pickup elements (112)such as a CCD. In this case, the function of the optical sensor can besubstituted for to some degree by newly installing a route by which theabsolute value of the light intensity can be acquired regardless of thegain that has been set for the image pickup elements. As a result, it isnot necessary to provide a new sensor, resulting in a reduced cost. Inaddition, if there is a margin in the processing time, a method oftaking in an image with a gain of 0, i.e., that is not amplified at all,in the intervals of image taking in for identification and calculatinginformation corresponding to the output value of the optical sensor onthe basis of this image is also conceivable. According to this method,the interval of taking in the image for identification becomes long, buta new hardware configuration becomes unnecessary.

If the finger is detected correctly by the gain control (304),subsequently picture quality control is exercised so as to obtain bloodvessel pattern most clearly, by suitably combining two modes, i.e., amode A for controlling the power of the light sources 114 (308) and amode B for controlling the sensitivity of the camera (314) according tothe situation. Specifically, the control is exercised in the followingtwo stages. First, the sensitivity of the camera is kept sufficientlyhigh, and picture quality control using the mode A is exercisedpreferentially (308). If the light quantity is too large and asufficient picture quality cannot be obtained even when the power of thelight sources 114 is set to 0 (310 to 312), the sensitivity of thecamera is controlled (314). Owing to such priority assignment, it ispossible to obtain a clear image of the blood vessel pattern bytransmitting a sufficient quantity of light through the finger. At thesame time, the sensitivity of the camera is prevented from being loweredthan needed, and consequently noise is prevented from being easilysuperposed on the image. In addition, since the intensity of the lightsources to be supplied to provide the same picture quality can be helddown, the electric power can be saved. If an optimum picture quality isobtained by exercising the above-described controls, a featureextraction (316) is conducted using the obtained image, and collation ofan obtained feature pattern with previously registered feature patterns(318) is conducted. If the obtained feature pattern coincides with aregistered feature pattern (320), the processing proceeds to anidentification success process 326 and corresponding processing such asunlocking is conducted. In the case of noncoincidence, the processingreturns to 308 and the processing beginning with the picture qualitycontrol is repeated. In addition, time elapse from the detection of thefinger is measured. If the identification has not succeeded within apredetermined time (322), the processing proceeds to an identificationfailure process 324, in which corresponding processing such as alarmissuing may be conducted. When processing is not conducted normally,therefore, it becomes possible to cope with this separately.

Hereafter, details of the picture quality control will be described.First, the gain of the camera optimized for the finger detection isaltered to that for feature extraction. Since the finger has beenalready detected at this point in time, it can be premised that thefinger is present certainly. Therefore, the gain is controlled so as tocause a region in an image that should emit intense reflected lightbecause of existence of the finger and light irradiated from theauxiliary light source to have predetermined brightness when theauxiliary light source 122 is on and cause the same region to havepredetermined darkness when the auxiliary light source 122 is off. Thisis the initial state of control.

As for the finger identification apparatus of the open type shown inFIG. 1, a light source power control method for obtaining a clear imageof the blood vessel pattern of the finger under external light isdescribed in US2004/0184641. Basically, the light sources disposed onthe left and right sides of the finger are set so as to cause the leftlight sources to become intense and the right light sources to becomeweak, and an image is acquired. Conversely, an image is acquired withthe left light sources caused to become intense and the right lightsources caused to become weak. Thus, two images are picked up. A lefthalf and a right half are selected respectively from the two images, andcombined. Even if a saturated highlight region occurs in a half of eachpicked up image located near the intense light sources, the remaininghalf has a clear image. Therefore, an image that is clear as a whole isobtained by combining clear half images. FIG. 4 shows an example inwhich the left light sources 114 are on and the right light sources areoff. In a region 400 that is the left side of the finger 102, a regionincluding a saturated highlight region occurs. As the location advancesto the right, the brightness becomes dark. In the right half, asaturated highlight region is not present. However, there is differencein finger among individuals. Even under the same light source power,therefore, the brightness of the half that is not located on the lightsource side becomes insufficient in the case of a thick finger, and thebrightness becomes excessive in the case of a thin finger. Such aproblem is eliminated by controlling the outputs of the light sources.

In the case where intense external light is irradiated to the finger,the external light plays the same role as the light sources, resultingin a state resembling the state in which the light sources are on. Evenif one of the left and right light sources is completely off, asaturated highlight region occurs even in a half opposite to the lightsources turned on according to the intensity or way of striking ofexternal light, and it becomes difficult to extract the blood vesselpattern. In the present embodiment, therefore, the picture quality isimproved by adaptively combining and controlling the light source powerand sensitivity of the camera. In the control, it is necessary toexercise feedback control between the picture quality of the picked upimage and the preset light source power value. If the whole of thepicked up image is designated as the subject of picture quality,however, the finger portion is not controlled to have a correct picturequality under the influence of brightness of the background portionother than the finger. Therefore, a region occupied by the finger isextracted from the image, and only the region is designated as thesubject of picture quality (310). First, therefore, a contour line ofthe finger is extracted by conducting image processing on the imagepicked up by the camera 112. As to the contour extraction, variousconventional techniques are known, and consequently they will not bementioned in detail. In the inside of the extracted contour line, aregion 402 on the side remote from light sources that are on isdesignated as the subject of the picture quality decision. In otherwords, the place where the light from the light sources that are on ismost hard to reach is selected. Specifically, it is desirable to selecta region located near an area between a middle line drawn between acenter line of the finger and the contour line, and the contour line.The tip and the root of the finger are remote from the light sources,and light does not arrive at them in some cases. If a region obtained byexcluding regions near the tip and the root of the finger is utilized,therefore, it is easy to obtain desired performance. The reason why thevicinity of the contour is selected will now be described. In thevicinity of the finger, the thickness of the finger is thin and thequantity of external light lost when the external light is transmittedthrough the finger is little. If the external light is intense,therefore, a saturated highlight region first occurs in the vicinity ofthe contour and a problem in the blood vessel pattern tends to occur inthe vicinity of the contour. For this reason, the vicinity of thecontour is selected. If a saturated highlight region occurs in theregion 402, it is meant that the external light is intense andconsequently the power of the light sources that are on is firstlowered. And the mode (mode B) for preferentially controlling thesensitivity of the camera is entered.

FIG. 6 is a flowchart specifically showing this processing. FIG. 6 showsan example of details of 308 to 314 shown in FIG. 3. First, the contourof the finger is extracted, and a region inside the finger is determined(600). And basically, a shift to the mode (mode A) for preferentiallycontrolling the light source power is conducted, and the processingproceeds to a process 616. If a saturated highlight region is seeninside the finger on the side of the light sources that are off althoughthe light sources on the side are off, or the output value of theoptical sensor 120 indicates that external light is intense, then it ismeant that the influence of external light is obviously strong. In sucha case, it is possible to set the light source power to a lowest valuethat can be set, make a shift to the camera sensitivity control mode,and proceed to the side of a process 606. By preparing such ashort-circuit route, the picture quality control can be exercised athigh speed. In the case where an optical sensor is used, the convergencespeed of the picture quality control is further raised by, for example,supposing a parameter that indicates whether the external light isintense, according to the output value of the optical sensor, andexercising control.

In the light source power control mode beginning with the process 616,the light source output is controlled so as to optimize the picked upimage according to the above-described light source power controltechnique. First, as described above as the process 310, it is checkedwhether average brightness of the finger image region 402 is in a targetrange (616). If the average brightness is lower than the target (618),the light source power is raised (620). If the average brightness ishigher than the target (618), it is checked whether the light sourcepower can be further lowered (622). If possible, the light source poweris lowered (624). If a saturated highlight region is seen, or morespecifically pixels having the saturated luminance are seen collectivelynear the contour line of the finger even when the light source power isset to its lowest output, a shift to the sensitivity control mode isconducted and then the sensitivity of the camera is further lowered(610).

In the camera sensitivity control mode, the method described as theprocess 310 is used in the same way as the light source power controlmode. It is checked whether average brightness of the finger imageregion (402) on the side opposite to the light sources that are on is inthe range of the target (606). If the average brightness is higher thanthe target (608), the sensitivity of the camera is lowered (610). If theaverage brightness is lower than the target, it is checked whether thesensitivity can be further raised (612). If possible, the sensitivity israised (614). 10′ If the target value is not yet reached although thesensitivity of the camera is set to a highest value that can be set,there is a limit in the image pickup using the sensitivity controlalone. Therefore, the light source power is raised (620), and a shift tothe light source control mode is conducted.

In the above-described flow, the upper limit is provided in thesensitivity control range of the camera. If the upper limit is exceeded,a shift to the light source power control is conducted. This is acontrivance for ensuring the picture quality. It is possible to attainthe average luminance that is nearly equal to that obtained by raisingthe light source power, by raising the sensitivity of the camera. If atthe same average luminance the case where the light source power israised is compared with the case where the sensitivity of the camera israised, a higher picture quality is frequently obtained in the casewhere the light source power is raised. Because noise caused in thepicked up image is obviously less when picking up an image usingsufficient light moderately as compared with when amplifying less lightand picking an image. This is one reason why the processing proceedsfrom the process 600 in the flow preferentially to the process 616 inthe light source power control mode.

In addition, there may be a case where the sensitivity is set to a verylow value at the time of, for example, initial state setting after thefinger detection and the light source power is insufficient even if itis maximized. In this case, it is also possible to cope with this byfurther providing a step for shifting from 620 to 612. In the same way,there may also be a case where the range of the target is not yetarrived at even if the light source power is maximized, because of theupper limit provided in the sensitivity control range. For that case aswell, a new route may be provided as hereafter described. In the lightsource power control mode, it is ascertained that the target is notreached even if the light source power is maximized. In addition, theupper limit of the sensitivity control range of the camera istemporarily raised to an upper limit that can be mechanically set as thecamera, or an upper limit at which degradation in picture quality causedby noise incurred at the time of high sensitivity image pickup does notexert a bad influence on identification precision. Then, a shift to thesensitivity control mode is conducted. As a result, the control range ofthe picture quality can be expanded so as to include the differenceamong individuals such as a finger that does not transmit light easily.The processing heretofore described is repeated. When the brightness ofthe finger has come in the range of the target, the picture qualitycontrol is finished (626).

If a necessary and sufficient quantity of light is supplied to thefinger by the flow, external light is preferentially used as the lightsource for image pickup and it becomes possible to reduce the energyconsumption in the light sources. As for the method for controlling thesensitivity of the camera, there is also a method of controlling theexposure time of the image pickup elements, besides the method ofcontrolling the gain for the output of the image pickup elements. If alens can be controlled, the iris may also be controlled optically.

In the foregoing description, it has been supposed that the lightsources on the left side shown in FIG. 4 are on. Conversely, if thelight sources on the left side are off and the light sources on theright side are on, processing similar to that described above isconducted by regarding the region 400 as the subject of the picturequality decision. As a result, it is possible to always pick up an imageof the finger with an optimum picture quality without depending upon theintensity of external light, and a clear blood vessel pattern isobtained. By the way, if the sensitivity of the camera is sufficientlyhigh and the necessary and sufficient quantity of external light ispresent, it is also possible to acquire the blood vessel pattern byexercising the sensitivity control alone of the camera without using thelight sources 114 at all. If use in an environment where external lightis always irradiated is considered, a configuration that does notincorporate the light sources 114 in the apparatus from the beginning isalso possible. For example, in an environment where an intense spotlight is always applied to the identification apparatus, such a way touse is also possible.

If external light streaming into the camera unit is intense, there is afear that the external light reflected by an internal mechanicalcomponent in the internal configuration of the apparatus shown in FIG. 1will pose a problem in the feature extraction. For example, as forexternal light streaming from the opening 110, light reflected by thetip of the lens barrel of the camera and returned to the finger isdifferent in surface reflectance of mechanical components and opticalpath length from light reflected by the bottom of the camera andreturned to the finger. Therefore, a difference between brightness anddarkness occurs and a light pattern is generated on the finger. Sincethis pattern is similar to the blood vessel pattern, this pattern isincluded in the extracted pattern. As a result, the extracted patternbecomes different from the blood vessel pattern registered under theordinary external light, resulting in an identification failure. FIG. 5shows an example in which a partition 500 is provided within theapparatus 100 between the opening 100 and the camera. The partition 500excludes internal mechanical components other than the opening 110 andthe opening of the camera from a space surrounded by the partition.Owing to the smooth surface shape free of differences in level andprojections, it is possible to prevent a pattern from being generated byreflection of external light. In the present embodiment, the opening(lens) of the camera is stuck to a hole 502 formed through the partitionso as to have a size just enough to pick up an image of a necessaryportion of the finger, without differences in level. In addition, theinside of the partition is covered by a material or paint that absorbsnear-infrared light to suppress the reflection itself. Differences inlevel similar to annual rings are provided in the barrel of the lens insome cases for a reason such as enhancing the light-gatheringperformance. Since these differences in level cause a pattern betweenbrightness and darkness, however, it is desirable that these differencesin level are not provided. In addition, it is more desirable to providecoating using a material or paint having a high infrared lightabsorption property, in the lens as well.

The energy intensity of sunlight is very high. In some cases, therefore,the range of optical energy that can be accepted by the camera isexceeded, and even the sensitivity control cannot be exercised. FIG. 7is a graph nearly representing the energy intensity of sunlight at theground surface every wavelength. However, it is appreciated that energyis scattered over various wavelengths. A wavelength range required topick up an image of a blood vessel pattern is limited between 700 nm and1000 nm. A living body tissue transmits well only light in thiswavelength region, and hemoglobin in blood absorbs well light in thiswavelength region. Therefore, differences between the blood vesselportion and other living body tissues are imaged clearly. As a result,the blood vessel pattern is formed. Therefore, the total quantity ofenergy incident on the camera can be decreased by attaching a band passfilter that passes through only the wavelength range to the camera. Evenif the bandwidth is limited, the energy quantity in the necessarywavelength region is not changed and consequently the picture quality isnot degraded. As the band is narrowed down, the total quantity of energyis decreased. However, it is necessary that identification can beconducted even in an environment where external light is not present andit is very dark. At that time, it is necessary to pick up an image withthe light sources turned on. Therefore, it is desirable to set the bandof the filter so as not to cut the effective wavelength region of thelight sources, especially the wavelength region having high energyintensities. As a result, the all-round sensitivity control becomespossible whether it be under intense sunlight or on a dark night.

FIG. 8 shows an example of a different filter for suppressing theinfluence of intense external light. This filter has a shape in whichpartition plates are provided in a box in a grid form. In FIG. 8, verylarge and high grids are shown. By providing the filter with a shapeformed by arranging a large number of minute grids that areindiscernible to the naked eye, however, it is possible to prevent gridlines from being imaged in the picked up image as they are. Owing to theexistence of the grid-like plates, it is possible to pass through onlylight perpendicular to the filter and cut light in an oblique direction.By mounting this filter between the camera and the finger, it becomespossible to pass through only light for picking up an image of the bloodvessel pattern emitted from the finger and prevent external light, suchas light in the oblique direction and light reflected in the apparatus,from arriving at the camera. As the present filter, a film that is thesame, in principle, as the film used to prevent the screen of theportable telephone from being watched from the flank can be used, and itis easily available.

FIG. 9 shows an example in which the present apparatus 100 is attachedto an instrument panel 902 of an automobile. An engine start button 900is used as the blood vessel identification start button 118 as well.With an operation for ordering the engine start, identification of theperson himself or herself can be conducted. If the identification issuccessful, the immobilizer is canceled and the engine is started. Ifthe identification is unsuccessful, the engine is not started. Since theidentification can be conducted in the natural operation for the enginestart, the burden imposed on the user is also lightened. When conductingmobile commerce, such as receiving service or purchasing commodities,via a communication network in cooperation with a car navigation system904, it is also possible to use the present apparatus as theidentification means for conducting settlement of accounts more safelyand certainly. For example, identification is conducted by holding up afinger over the present apparatus instead of the conventional inputtingof a secret identification number. As a way of cooperation, it is alsopossible to display guidance for the identification method of thepresent apparatus by using the screen of the car navigation system.

FIG. 10 shows an example in which the present apparatus 100 is attachedto a door handle 1000 of an automobile. When opening the door, the dooris unlocked by conducting the blood vessel identification using thepresent apparatus. The identification start button 118 is used as a doorlock button as well. When locking the door, the door is locked bypressing the button 118. In the case of locking, it is not necessary toespecially conduct the identification of the person himself or herselffrom the viewpoint of security. Therefore, the locking may be conductedby only pressing the button 118 even if the identification isunsuccessful. In alternative implementation, the button 118 is pressedin a correctly identifiable form. If the identification of the personhimself or herself is successful, the data is stored together withordinary registered data as one of latest registered data. The storeddata can be handled as registered data to be referred to when unlockingthe next time. Even in an unstable environment where an obtained featuretends to differ from that obtained at the time of registration becauseof, an environment of the automobile, an extreme change in the healthstate, an injury, or a change in the way of placing the finger,therefore, the safety of the identification can be improved because thelatest data can also be referred to. Furthermore, a cover 1002 can alsobe attached to the identification apparatus. Even if the automobile isplaced outdoors and tends to be weather-beaten, it is possible toprevent dirt or dust from damaging the apparatus and making theidentification unstable.

The identification apparatus has heretofore been described by taking afinger blood vessel identification apparatus of open type taking a shapethat can take in external light most easily, as an example. However, itis a matter of course that the above-described technique forimplementing the stabilization of the picture quality of picked up imageand reduction of the energy consumption in the light sources byexercising the power control of light sources for image pickup and thesensitivity control of the image pickup system synthetically can beapplied to finger blood vessel identification apparatuses having adifferent form and other biometric schemes in which an image of a livingbody is picked up using light to conduct personal identification.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A personal identification apparatus comprising: an image pickup unitfor picking up an image by using light transmitted by a finger; and aprocessing unit for conducting personal identification by extractingblood vessels from an image picked up by said image pickup unit,wherein: said processing unit detects that the finger exists in apredetermined position, and extracts a region occupied by the fingerfrom the picked up image, and said processing unit controls a lightsource power control unit for changing power of light sources and/or asensitivity control unit for changing an amplification factor of imagepickup elements in said image pickup unit, on a basis of information inthe extracted region.
 2. The personal identification apparatus accordingto claim 1, wherein: said processing unit determines whether a quantityof light irradiated to the finger is within a predetermined range, on abasis of the information in the extracted region, when the quantity oflight irradiated to the finger is judged to be outside the predeterminedrange, said processing unit determines whether the quantity of lightirradiated to the finger can be caused to be within the predeterminedrange by controlling the light source power control unit, and when it isjudged that the quantity of light irradiated to the finger cannot becaused to be within the predetermined range, said processing unitcontrols the sensitivity control unit.
 3. The personal identificationapparatus according to claim 1, wherein: when the quantity of lightirradiated to the finger is judged to be larger than the predeterminedrange, said processing unit lowers power of the light sources via thelight source power control unit, and when the quantity of lightirradiated to the finger is judged to be smaller than the predeterminedrange, said processing unit raises power of the light sources via thelight source power control unit.
 4. The personal identificationapparatus according to claim 2, wherein: when the quantity of lightirradiated to the finger is judged to be larger than the predeterminedrange, said processing unit lowers power of the light sources via thelight source power control unit, and when the quantity of lightirradiated to the finger is judged to be smaller than the predeterminedrange, said processing unit raises power of the light sources via thelight source power control unit.
 5. The personal identificationapparatus according to claim 3, wherein: when the quantity of lightirradiated to the finger is judged to be large even if the power of thelight sources is minimized, or when the quantity of light irradiated tothe finger is judged to be small even if the power of the light sourcesis maximized, said processing unit controls a sensitivity of said imagepickup unit via the sensitivity control unit.
 6. The personalidentification apparatus according to claim 1, wherein: the lightsources irradiate light to the finger alternately from left and rightdirections, and said processing unit uses information in a partialregion located on a side of light sources that are off, in the extractedregion.
 7. The personal identification apparatus according to claim 1,wherein: said processing unit detects existence of the finger on a basisof a change of the image picked up by a camera with time.
 8. Thepersonal identification apparatus according to claim 2, wherein: saidprocessing unit detects existence of the finger on a basis of a changeof the image picked up by a camera with time.
 9. The personalidentification apparatus according to claim 7, further comprising anauxiliary light source, wherein said processing unit detects existenceof the finger on a basis of an image picked up using light irradiated bysaid auxiliary light source.
 10. The personal identification apparatusaccording to claim 1, further comprising an optical sensor, wherein saidprocessing unit calculates a gain value on a basis of a result ofmeasurement conducted using said optical sensor, controls a sensitivityof said image pickup unit via the sensitivity control unit so as toattain the gain value, and conducts the finger detection.
 11. Thepersonal identification apparatus according to claim 2, furthercomprising an optical sensor, wherein said processing unit calculates again value on a basis of a result of measurement conducted using saidoptical sensor, controls a sensitivity of said image pickup unit via thesensitivity control unit so as to attain the gain value, and conductsthe finger detection.
 12. The personal identification apparatusaccording to claim 1, wherein: an opening provided between the fingerand the camera, and an opening of the camera are surrounded by apartition formed of smooth surfaces, and other internal components areprovided outside the partition.
 13. The personal identificationapparatus according to claim 1, wherein: the personal identificationapparatus is attached to a part of an automobile, and if the personalidentification is successful, control of the automobile becomespossible.